The present invention relates to a method of preparing alumina hydrosol from an aluminum sulfate solution (alum solution). Alumina hydrosol is a well-known starting material for the preparation of alumina and alumina-containing refractory oxide composites such as alumina-silica. Such refractory oxides are useful as adsorbents and particularly as catalysts or catalyst supports. The general technique of preparing alumina hydrosols by digesting aluminum metal in a mineral acid is well documented in the literature and prior art; with respect to hydrosol preparation, as well as other aspects of alumina manufacture; the reader's attention is directed to U.S. Pat. Nos. 2,620,314, 2,666,749, 2,689,226, 2,774,743, and 3,020,242 for a thorough background of the subject matter.
As the cost of the aluminum metal used in the hydrosol preparation method becomes more expensive the use of relatively inexpensive aluminum salts to substitute for aluminum metal becomes an economically attractive alternative.
Large quantities of aluminum sulfate are produced as a by-product of spent catalyst metals recovery processes. U.S. Pat. No. 2,787,540, for instance, discloses a spent catalyst metals recovery process wherein a deactivated alumina platinum catalyst is treated with sulfuric acid which results in the formation of aluminum sulfate as a by-product. In view of the existence of this relatively inexpensive source of aluminum there has been a heretofore unfulfilled long felt demand to utilize this source in the manufacture of acidic aluminum hydrosols.
Accordingly, it would be economically desirable to recycle the by-product aluminum sulfate to an alumina hydrosol from which hydrosol may be employed to produce alumina or alumina-containing compositions.
U.S. Pat. No. 3,066,012 teaches a process for preparing alumina gels from alum solutions wherein an aqueous slurry of calcium carbonate is added to the alum solution, a resulting basic aluminum sulfate hydrosol is recovered, and an alumina gel is formed by adding sodium carbonate to the basic aluminum sulfate hydrosol.
In contradistinction to the above-described process the method of the present invention recovers the aluminum from an alum solution in the form of an acidic alumina hydrosol which hydrosol is substantially free of sulfate impurities.